For reasons such as the presence of the restriction that the localities of natural gas are usually distant from cities or other industrial facilities, natural gas liquefaction plants for purifying and liquefying the natural gas that was mined from gas fields are commonly self-sufficient at the plant site in terms of the quantitative motive power requirement for plant operation. With this as the background, gas turbine equipment fueled by the mined natural gas is often used as the motive power supply equipment for the natural gas liquefaction plants (refer to Japanese Patent Application Publication JP-A-2003-515720 and other documents).    Patent Document 1: JP-A-2003-515720